Forklift trucks have been used either to lift goods of relatively heavy weight up to an elevated location or to lower the goods on the ground. The forklift trucks also can be used to move the goods from one place to another within a limited working area. Depending on the power sources employed, the forklift trucks are classified into an engine-driven forklift truck which may usually operate in an outdoor area and an electromotive forklift truck which are suitable for indoor operation, thanks to its reduced or little emission of exhaust gas and noise.
It is well known in the art that the electromotive forklift truck includes an electric travel motor whose speed and direction is controlled by a controller in response to external command signals. In addition to the electric travel motor, the electromotive forklift truck is provided with a variety of electric components that have the possibility of failure during their use. Since the failure of the electric components will make the forklift truck inoperable, it would be desirable to provide means for diagnosing and displaying the condition of the electric components in an efficient fashion so that the operator or repairman can take appropriate measure.
Background concerning a conventional method for diagnosing the forklift truck can be found in U.S. Pat. No. 4,521,885 by Melocik et al. The Melocik et al patent teaches a method for diagnosing the forklift truck in sequential order when the mode selector is in a diagnostic position. The diagnosing steps are predetermined by a software program.
However, the conventional diagnostic method has a disadvantage that it takes too long time to carry out the diagnosis, since the diagnosing procedure is automatically executed up to a final check point according to a programed schedule in sequential order even though the operator wants to give up halfway the diagnosis.
Additionally, the conventional diagnostic method poses a problem that the operator should repeatedly ascertain the resultant test code on the display during the period of test as the test code is temporarily displayed on the display each time a single sort of test is completed. Another problem of the conventional diagnostic method is that the operator can not initiate the test mode quickly during the run mode, since test switches need to be actuated in order to perform the in-service test.